Unesterified (free) cholesterol is a major component of plasma membranes of eukaryotic cells and plays many roles in regulation of the biochemical and physiological properties of cells. Fluorescent spectroscopy and fluorescence microscopy have been frequently applied to study lipid-lipid and lipid-protein interactions in model membranes, cell membranes, and plasma lipoproteins.
Current fluorescent analogs of free cholesterol are inadequate. For example, analogs of unesterified cholesterol bearing a N,N-dimethylaminonaphthalenesulfonate (dansyl), pyrene, or a 7-nitrobenz-2-oxa-1,3-diazolyl-4-amino (NBD) moiety are not faithful mimics of free cholesterol as they are not capable of partitioning into liquid-ordered domains under conditions in which free cholesterol is known to partition into such domains. Thus, the existing fluorescent probes of free cholesterol are not adequate for studying the binding of free cholesterol to other lipids and to proteins and glycoproteins and for monitoring the dynamics of free cholesterol movement within membranes, cells, and lipoproteins.
As a result, new fluorescent analogs of free cholesterol are needed that mimic the physical behavior of free cholesterol in membranes and have desirable spectroscopic properties and physical properties for use in fluorescence studies with cells and model membranes. Likewise, new compounds are needed for examining whether the formation of membrane lipid domains (rafts) affect the physical and biochemical properties of cells.